In recent years, much attention has been paid to respiratory complications of transfusion. Transfusion related acute lung injury (TRALI) is defined as an acute lung injury that is temporally associated with blood transfusion. TRALI is one of the leading causes of mortality. Although the etiology of TRALI is not fully understood, one of its main causes is thought to be anti-leukocyte antibodies, such as HLA antibody or HNA antibody. A precautionary male-predominant plasma strategy has been implemented in many developed countries, which has resulted in considerable achievements in reducing the incidence of TRALI. Meanwhile, transfusion-associated circulatory overload (TACO) has emerged as a major differential diagnosis of TRALI. TACO is a well-known complication of transfusion, which has been considered not as a side effect of transfusion but a result of erroneous medical practice. It has long been an under-reported complication of transfusion and has not been investigated scientifically. Recent data on transfusion mortality from the Food and Drug Administration revealed that TACO was the second highest cause of death in the United States. Our data also suggested a steep increase in the reported cases of TACO in Japan. Precautionary measures should also be implemented for this emerging complication.